Electronic devices having pixels with elevated fill factors

ABSTRACT

An electronic device with a display may be provided with an array of pixels each of which includes subpixels formed from organic light-emitting diodes. The electronic device may have support structures such as a head-mountable frame or other head-mountable support structure. Optical structures such as lenses may be provided through which the array of pixels is viewable by a user. The array of pixels and the lenses or other optical structures may be supported by the head-mounted support structure. Light spreading structures may overlap the array of pixels to enhance the fill factor of the pixels. The light spreading structures may be formed from a fiber bundle layer, an array of microlenses, or other optical structures that laterally spread light that has been emitted by the organic light-emitting diodes and thereby enhances the fill factor of the pixels.

This application claims the benefit of U.S. provisional patentapplication No. 62/466,668, filed on Mar. 3, 2017 which is herebyincorporated by reference herein in its entirety.

BACKGROUND

This relates generally to displays and, more particularly, tohead-mounted displays.

Head-mounted displays may have display panels and lenses. Lenses may beused to magnify images displayed on a display panel. If care is nottaken, the images that are presented to a user of a head-mounted displaywill contain visual artifacts. For example, display panels may besubject to unwanted screen door effects. Screen door effects occur whenpixels have low fill factors and can be intensified when images aremagnified using lenses in a head-mounted display.

SUMMARY

A head-mounted display such as a virtual reality headset may be providedwith a pixel array formed from a display panel with an array of organiclight-emitting diodes. The pixel array may be mounted to a head-mountedsupport structure. Optical structures such as lenses may also be mountedto the head-mounted support structure. Images on the pixel array may beviewed by a user through the optical structures.

The fill factor of the pixels in the pixel array may be enhanced byforming light spreading structures over the organic light-emittingdiodes. The light spreading structures may laterally spread light thatis being emitted by the organic light-emitting diodes and may therebyincrease the fill factor of the pixels an enhanced value such as 90% ormore.

The light spreading structures may be formed from a fiber bundle layer,an array of microlenses, or other optical structures that are configuredto laterally spread emitted light from the organic light-emitting diodesin the pixels. A fiber bundle layer may be formed from a layer of fiberseach of which overlaps a respective one of the pixels. An array ofmicrolenses may be formed on the pixel array so that each microlensoverlaps one, two, three, or other suitable number of organiclight-emitting diodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an illustrative head-mounted display inaccordance with an embodiment.

FIG. 2 is a diagram of an illustrative pixel array in a head-mounteddisplay in accordance with an embodiment.

FIG. 3 is a cross-sectional side view of an illustrative organiclight-emitting diode display for a device such as a head-mounted displayin accordance with an embodiment.

FIG. 4 is a top view of an illustrative pixel having subpixels of threedifferent colors in accordance with an embodiment.

FIG. 5 is a top view of an illustrative fiber bundle layer in accordancewith an embodiment.

FIG. 6 is a cross-sectional side view of an illustrative display such asan organic light-emitting diode display with a fiber bundle layer inaccordance with an embodiment.

FIG. 7 is a cross-sectional side view of an illustrative display such asan organic light-emitting diode display having pixels with microlensesfor enhancing fill factor in accordance with an embodiment.

FIGS. 8 and 9 are top views of illustrative subpixel patterns fordisplays with microlenses in accordance with an embodiment.

DETAILED DESCRIPTION

Head-mounted displays may be used for virtual reality and augmentedreality systems. For example, a virtual reality headset that is worn onthe head of a user may be used to provide a user with virtual realitycontent.

An illustrative system in which a head-mounted display is used inproviding a user with virtual reality content and/or augmented realitycontent is shown in FIG. 1. As shown in FIG. 1, head-mounted display 10may include a display such as display 14 (sometimes referred to as adisplay panel or pixel array). Display 14 may be mounted to frame 12 orother head-mountable support structures that allow display 14 to bemounted on the head of a user.

Display 14 may have an opaque substrate or may be transparent. Anysuitable display technology may be used in forming the pixels of display14. As an example, display 14 may be an organic light-emitting diodedisplay or other display having an array of organic light-emitting diodepixels that display images for viewer 18. Images on the pixel array ofdisplay 14 may be viewed by user's eyes 18 through an optical systemsuch as optical system 16. Optical system 16 may be mounted to frame 12or other head-mounted display support structures.

Optical system 16 may include one or more lenses. For example, opticalsystem 16 may include a first lens that focuses images on a left-handportion of display 14 for viewing by a left-hand user's eye 18 and mayinclude a second lens that focuses images on a right-hand portion ofdisplay 14 for viewing by a right-hand user's eye 18.

If desired, head-mounted display 10 may have beam splitters and/or otheroptical combiners that are used to merge real-world images with imagesfrom display 14 (e.g., to provide a user with an augmented realityexperience), display 10 may include one or more cameras to captureimages that are displayed on display 14 (e.g., for augmented reality),head-mounted display 10 may be a virtual reality headset (e.g., display14 may be opaque and/or may be mounted in opaque portions of supportstructure 12 that block ambient light), and/or other configurations maybe used for head-mounted display 10. The configuration of FIG. 1 ismerely illustrative.

Display 14 may be based on a liquid crystal display, an organiclight-emitting diode display, a display having an array of crystallinesemiconductor light-emitting diode dies, and/or displays based on otherdisplay technologies. Separate left and right display panels may beincluded in head-mounted display 10 for the user's left and right eyesor a single display panel may span both eyes 18.

Visual content (e.g., image data for still and/or moving images) may beprovided to display 14 using control circuitry that is mounted inhead-mounted display 10 and/or control circuitry that is mounted outsideof head-mounted display 10 (e.g., in an associated portable electronicdevice, laptop computer, or other computing equipment). The controlcircuitry may include storage such as hard-disk storage, volatile andnon-volatile memory, electrically programmable storage for forming asolid-state drive, and other memory. The control circuitry that providesimages for displaying on display 14 of head-mounted display 10 may alsoinclude one or more microprocessors, microcontrollers, digital signalprocessors, graphics processors, baseband processors,application-specific integrated circuits, and other processingcircuitry. Communications circuits in head-mounted display 10 may beused to transmit and receive data (e.g., wirelessly and/or over wiredpaths).

Control circuitry in head-mounted display 10 may use display 14 todisplay visual content such as virtual reality content (e.g.,computer-generated content associated with a virtual world),pre-recorded video for a movie or other media, or other images.Illustrative configurations in which the control circuitry ofhead-mounted display 10 provides a user with virtual reality contentusing display 14 may sometimes be described herein as an example. Ingeneral, however, any suitable content may be presented to a user by thecontrol circuitry of head-mounted display 10 using display 14 andoptical system (lenses) 16.

FIG. 2 is a diagram of an illustrative display such as display 14 ofFIG. 1. Display 14 may include a source of images such as pixel array20. Pixel array 20 may be formed from a two-dimensional array of pixels22 (e.g., organic light-emitting diode pixels, liquid crystal displaypixels, etc.). Pixels 22 may be arranged in rows and columns. Columns ofpixels 22 may be provided with data over data lines D. Rows of pixelsmay be controlled using horizontal control signals (sometimes referredto as scan signals, emission enable signals, gate line signals, etc.)that are provided to the pixels using one or more gate lines G in eachrow.

Control circuitry in head-mounted display 10 may provide display 14 withimage data via path 24. Display 14 may include display driver circuitry26. Display driver circuitry 26 may include data line (column) drivercircuitry 26A and gate line driver circuitry 26B. Circuitry 26A and 26Bmay be formed using one or more integrated circuits and/or thin-filmtransistor circuitry. With one illustrative configuration, drivercircuitry 26A may receive image data via path 24 and may providecorresponding data signals to columns of pixels 22 via data lines Dwhile supplying clock and control signals to gate line driver circuitry26B. Gate line driver circuitry 26B may supply gate line control signalsto rows of pixels 22 based on the clock and control signals receivedfrom display driver circuitry 26A. There may be gate line drivercircuitry 26B on one or more edges of pixel array 20. For example, gateline driver circuitry 26B may be formed on the left-hand edge of display14 and/or gate line driver circuitry 26B′ may be formed on theright-hand edge of display 14.

To reduce weight and ensure that head-mounted display 10 is compact andnot too bulky, it may be desirable to form display 14 from lightweightdisplay structures such as a lightweight organic light-emitting diodedisplay panel or a lightweight display panel having an array oflight-emitting diodes formed from respective crystalline semiconductordies (as examples). A cross-sectional side view of an illustrativeorganic light-emitting diode display formed from thin-film circuitry isshown in FIG. 3.

As shown in FIG. 3, display 14 may have a substrate such as substrate32. Substrate 32 may be formed from glass, polymer, and/or othermaterials. Thin-film circuitry 34 may be formed from layers ofdielectric, metal, and semiconductors and may include thin-filmcapacitors, interconnect lines, and thin-film devices such as thin-filmtransistor 36. For example, a layer of thin-film circuitry such ascircuitry 34 may include thin-film transistors that serve as switchingtransistors, emission enable transistors, drive transistors, and otherpixel circuit transistors. Thin-film layers may be deposited andpatterned on thin-film circuitry 34 to form organic light-emittingdiodes for pixels 22 such as illustrative light-emitting diode 30 ofFIG. 3.

Each light-emitting diode 30 may include a layer of organic emissivematerial 40 interposed between an anode such as anode 38 and a cathodesuch as cathode 42. Anodes 38 may be formed from a patterned metal layerdeposited on the upper surface of thin-film circuit layer 34. Cathode 42may be formed from a blanket conductive film (e.g., a film oftransparent conductive material such as indium tin oxide and/or a layerof one or more metals that is sufficiently thin to be transparent).Light-emitting diode 30 may be formed in an opening in pixel definitionlayer 44. Pixel definition layer 44 may be formed from a layer ofpolymer. Overcoat layer 46 may be formed from one or more transparentmaterials (e.g., polymer, inorganic materials, etc.). Overcoat layer 46may help planarize and protect the array of diodes 30 formed onsubstrate 32 (e.g., overcoat layer 46 may serve as an encapsulationlayer for thin-film circuitry such as diodes 30 and the circuitry oflayer 34).

During operation, transistors 36 may supply current to organiclight-emitting diodes 30 under the control of display driver circuitry26. This causes light-emitting diodes 30 to emit light 48 and causes thearray of pixels 22 in display 14 to display images for a user.

Each pixel 22 of pixel array 20 may include multiple subpixels. Thesubpixels may have light-emitting diodes of different colors (e.g., red,green, blue, light blue, yellow, etc.). As an example, each pixel 22 ofarray 20 may have a red subpixel, a green subpixel, and a blue subpixel.The red subpixels of display 14 may have red light-emitting diodes 30that contain red emissive material 40 and that emit red light 48, thegreen subpixels of display 14 may have green light-emitting diodes 30that contain green emissive material 40 and that emit green light 48,and the blue subpixels of display 14 may have blue light-emitting diodes30 that contain blue emissive material 40 and that emit blue light.Pixels with other numbers of subpixels and/or subpixels of differentcolors may be used, if desired.

A top view of an illustrative pixel having a blue subpixel B formed froma blue light-emitting diode, a green subpixel G formed from a greenlight-emitting diode, and a red subpixel R formed from a redlight-emitting diode is shown in FIG. 4. Each subpixel may emit light 48from the region overlapped by the anode 38 of the light-emitting diode30 in that subpixel. The rest of pixel 22 is covered by pixel definitionlayer 44 and does not emit light. In pixel 22 of FIG. 4, for example,blue light is emitted from the area overlapping the blue light-emittingdiode anode (the area labeled “B” in FIG. 4), red light is emitted fromthe area overlapping the red light-emitting diode anode (the arealabeled “R” in FIG. 4), and green light is emitted from the areaoverlapping the green light-emitting diode anode (the area labeled “G”in FIG. 4). The ratio of the diode areas (anode areas) emitting light 48to the total area of pixel 22 is referred to as the fill factor of pixel22. Low fill factor displays are characterized by relatively largefractions of pixel real estate that do not emit light and thereforecontribute to undesired screen door effects. If care is not taken, thefill factor of the pixels in an organic light-emitting diode display maybe relatively small (e.g., 20-30%), particularly in high resolutiondisplays of the type that may be desirable for use in head-mounteddisplays.

To minimize screen door effects and thereby enhance display quality fordisplay 14, pixels 22 of pixel array 20 in display 14 may be providedwith light spreading structures that enhance the fill factor for pixels22. The light spreading structures may be formed from microlenses, afiber bundle layer (sometimes referred to as a light guide bundle layeror light guide layer), or other optical structures that overlap pixelarray 20 and that laterally spread the light 48 that is emitted fromeach light-emitting diode. This enhances the fill factor for the pixelsof display 14 (e.g., the fill factor of display 14 may be at least 0.4,at least 0.5, at least 0.6, at least 0.7, at least 0.8, at least 0.9, atleast 0.95, or at least 0.98 even if the fill factor of the underlyinglight-emitting diode structures is less than 0.3 or other relativelysmall value).

Fiber bundles may be formed from a set of parallel transparent fibersbound together with a polymer or other binder material. The fibers may,for example, be formed from transparent polymer or glass. After bindingthe fibers together to form a fiber bundle, the fiber bundle may bedivided into individual fiber bundle layers by cutting the fiber bundleinto slices (slicing perpendicular to the lengths of the fibers) and bypolishing the cut slices. Fibers may have circular cross-sectionalshapes, rectangular (e.g., square) cross-sectional shapes, or othersuitable cross-sectional shapes. If desired, a bundle of light guidesmay be formed directly on the thin-film circuitry of a display (e.g.,using microfabrication techniques). Fiber bundle layers may also beformed separately and laminated to a pixel array using an adhesive layer(e.g., a transparent overcoat layer) or spaced apart from the display(e.g., by an air gap).

A top view of an illustrative fiber bundle layer is shown in FIG. 5. Asshown in FIG. 5, fiber bundle layer 50 may be formed from an array offibers 52 that have been bound together using binder 54. Fiber bundlelayer 50 may be relatively wide in lateral dimensions X and Y and may berelatively thin in vertical dimension Z. Layer 50 may be planar (e.g.,layer 50 may lie in the X-Y plane of FIG. 5) so that layer 50 may beplaced on the planar surface of pixel array 20.

During operation, light 48 from underlying light-emitting diodes 30propagates outwardly through fibers 52 in direction Z. This spreads thelight from each light-emitting diode 30 in dimensions X and Y so thatthe light fills the entire exposed face of an associated overlappingfiber 52. By lateralling spreading the light from light-emitting diodes30 before this light is viewed by the user, the fraction of displaysurface area that is consumed by dark areas (see, e.g., pixel definitionlayer 44 of FIG. 4) is minimized and fill factor is enhanced.

The light guiding properties of fibers 52 may be determined by therelative index of refraction values of fibers 52 and binder 54. Theindex of refraction of fibers 52 may be na and the index of refractionof binder 52 may be nb. With one illustrative configuration, the valueof nb may be less than na to promote light guiding within fibers 52(along the Z axis of FIG. 5) due to the principal of total internalreflection. The relative values of na and nb may be chosen so that thenumerical aperture of fibers 52 is 0.66, 0.6-0.7, 0.6-0.8, 0.5-0.8, morethan 0.5, less than 0.8, or other suitable value. It may be desirable tominimize the amount of area consumed by binder 54 relative to the amountof area consumed by fibers 52 in layer 50 to help minimize pixel fillfactor as light travels through fiber bundle layer 60. For example,binder 54 may consume less than 50% of the area of layer 50, less than30% of the area of layer 50, less than 15%, of the area of layer 50, orless than 5% of the area of layer 50 (as examples).

A cross-sectional side view of display 14 showing how fiber bundle layer50 may be formed on top of overcoat layer 46 of pixel array 20 is shownin FIG. 6. Pixel array 20 may include an array of pixels 22 formed onlayers(s) 60. Layers 60 may include thin-film transistor circuitry 34,substrate 32, and the other layers of display structures under overcoatlayer 46 that are shown in FIG. 3 (as an example).

Each pixel 22 may include a set of red, green, and blue light-emittingdiodes 30 that emits light 48. Light 48 is guided upwardly alongdimension Z within each overlapping fiber 52 and is emitted as light 60at the exposed upper face 52F of that fiber 52. In the example of FIG.6, there is a one-to-one relationship between the fibers 52 in layer 50and the pixels 22 of pixel array 20. If desired, there may be morefibers 52 than pixels 22 or more pixels 22 than fibers 52. As anexample, the density (number of fibers per unit area) of fibers 52 maybe larger than the density of pixels 22 (number of pixels per unit area)by a factor of at least 2, at least 4, at least 10, 2-10, at least 20,less than 1000, or other suitable amount. In some configurations, eachfiber 52 overlaps a respective subpixel in each pixel 22 or othersuitable subset of a pixel. In configurations in which the density ofpixels 22 is much larger than the density of pixels 22, each fiberoverlaps a relatively small fraction of a pixel and each pixel 22overlaps multiple fibers 52 (e.g., each pixel 22 overlaps 2-100 fibers52, 2-30 fibers 52, at least 2 fibers 52, at least 5 fibers 52, at least15 fibers 52, at least 30 fibers 52, fewer than 200 fibers 52, or othersuitable number of fibers). Dashed lines 52′ show how multiple fibers 52may overlap each pixel 22 (e.g., in a scenario in which the density offibers 52 is larger than the density of pixels and/or subpixels indisplay 14). If desired, some or all of overcoat 46 may be removed(e.g., to space the lower surfaces of fibers 52 by an air gap frompixels 22)

The thickness T of fiber bindle layer 50 is preferably sufficientlylarge to ensure that light 48 is homogenized (scrambled) whilepropagating upwardly in direction Z. For example, thickness T may be 0.5mm to 10 mm, 0.5 to 2 mm, at least 0.2 mm, at least 0.4 mm, at least 0.5mm, 0.5 to 2 mm, less than 5 mm, less than 1 mm, or other suitablethickness. The lateral X and Y dimensions (dimension WP) of each pixel22 and therefore the lateral X and Y dimensions (dimension WF) of eachfiber 52 may be 30-70 microns, at least 10 microns, at least 20 microns,at least 30 microns, less than 100 microns, less than 50 microns, lessthan 30 microns, or other suitable size. Fibers 52 may have circularcross sections, rectangular cross sections (e.g., square, square withrounded corners, etc.), or other suitable shapes.

FIG. 7 is a cross-sectional side view of display 14 in an illustrativeconfiguration in which light scattering structures have been formed frommicrolenses. As shown in FIG. 7, display 14 may include pixel array 20.Pixel array 20 may be formed form an array of pixels 22 on layer(s) 60(e.g., a substrate layer, one or more layers of thin-film circuitry,etc.). Each pixel 22 may contain red, green, and blue subpixels or mayinclude subpixels of other colors.

A patterned layer of microlenses 70 may be formed on pixel array 20. Asone example, each pixel 22 may be overlapped by a correspondingmicrolens 70. Configurations for display 14 in which each pixel 22 isoverlapped by a different number of microlenses 70 (e.g., more than onemicrolens per pixel) may also be used.

Lenses 70 and pixels 22 may have lateral dimensions X and Y of 30-70microns, at least 10 microns, at least 20 microns, at least 30 microns,less than 100 microns, less than 50 microns, less than 30 microns, orother suitable size. Light 48 that is emitted upwardly in direction Zmay be laterally spread and collimated by passing through lenses 70, asshown in FIG. 7. Lenses 70 may be formed from inorganic materials and/ororganic materials (e.g., transparent polymer).

Lenses 70 may be covered with transparent coating layer 72. Transparentcoating layer 72 may be formed from a polymer or other material havingan index of refraction n2 that is more than the index of refraction n1of lenses 70 so that lenses 70 act as negative lenses and help tocollimate (concentrate) emitted light towards user's eyes 18. Becauseeach lens 70 spreads light 48 laterally, light 48 will be emitted overportions of the surface of display 14 that otherwise would containnon-light-emitting structures such as portions of pixel definition layer44. Microlens 70 (or other light spreading structures such as fibers 52in fiber bundle layer 50) therefore spread light laterally so that pixelfill factor is enhanced and screen door effects in display 14 areminimized.

Illustrative microlens layouts for display 14 in which each microlenscovers a subset of a pixel are shown in FIGS. 8 and 9. In the example ofFIG. 8, each pixel 22 has a red subpixel formed from a red diode R, agreen subpixel formed from a green diode G, and a blue subpixel formedfrom a blue diode B and each of these subpixels is overlapped by acorresponding microlens 70. In the example of FIG. 9, the blue diode B(e.g., the blue anode area) that forms the blue subpixel of pixel 22 islarger than the red and green diodes R and G (to help compensate forweaker blue organic light-emitting diode light emission). In this typeof arrangement, a pair of microlenses 70 may overlap each bluelight-emitting diode and a single respective microlens 70 may overlapeach of the red and green light-emitting diodes. Other patterns ofmicrolenses and light-emitting diodes may be used in forming display 14if desired. For example, odd rows of pixel array 20 may containalternating red and green subpixels and even rows in pixel array 20 maycontain alternating green and blue subpixels, etc. In general, eachmicrolens 70 may overlap 1-3 subpixels, fewer than 4 subpixels, morethan 1 subpixel, or other suitable numbers of subpixels. The examples ofFIGS. 7 and 8 are merely illustrative.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. An electronic device with a display configured todisplay images viewable by a user, comprising: a head-mounted supportstructure; an array of pixels supported by the support structure,wherein the array of pixels is configured to produce light associatedwith the images; a fiber bundle layer that overlaps the array of pixels;and an optical system supported by the head-mounted support structurethrough which the images are viewable, wherein the array of pixels isformed from a layer of thin-film circuitry containing thin-filmtransistors, a layer of patterned anodes on the layer of thin-filmcircuitry, organic emissive material on the anodes, a cathode layer, andan overcoat layer and wherein the overcoat layer is interposed betweenthe fiber bundle layer and the cathode layer.
 2. The electronic devicedefined in claim 1 wherein the fiber bundle layer includes an array offibers and includes binder that binds the fibers together and whereinthe fibers each have a rectangular cross-sectional shape.
 3. Anelectronic device with a display configured to display images viewableby a user, comprising: a head-mounted support structure; an array ofpixels supported by the head-mounted support structure, wherein thearray of pixels is configured to produce light associated with theimages; an array of microlenses, each pixel overlapping at least onemicrolens; and an optical system supported by the head-mounted supportstructure through which the images are viewable, wherein the array ofmicrolenses is interposed between the array of pixels and the opticalsystem.
 4. The electronic device defined in claim 3 wherein the each ofthe pixels includes first, second, and third light-emitting diodes ofdifferent colors and wherein each microlens overlaps the first, second,and third light-emitting diodes of a respective one of the pixels. 5.The electronic device defined in claim 3 wherein each of the pixelsincludes first, second, and third light-emitting diodes of differentcolors, wherein each of the first light-emitting diodes is overlapped bya respective one of the microlenses, and wherein each of the secondlight-emitting diodes is overlapped by a respective one of themicrolenses.
 6. The electronic device defined in claim 5 wherein each ofthe third light-emitting diodes is overlapped by a respective one of themicrolenses.
 7. The electronic device defined in claim 5 wherein each ofthe third light-emitting diodes is overlapped by a respective pair ofthe microlenses.
 8. The electronic device defined in claim 7 whereineach of the third light-emitting diodes is a blue light-emitting diode.9. The electronic device defined in claim 3 further comprising a coatinglayer on the array of microlenses, wherein the microlenses have a firstindex of refraction and wherein the coating layer has a second index ofrefraction that is greater than the first index of refraction.
 10. Anelectronic device with a display configured to display images viewableby a user, comprising: a support structure; an array of pixels supportedby the support structure, wherein the array of pixels is configured toproduce light associated with the images; and a fiber bundle layer thatoverlaps the array of pixels, wherein the array of pixels is formed froma layer of thin-film circuitry containing thin-film transistors, a layerof patterned anodes on the layer of thin-film circuitry, organicemissive material on the anodes, a cathode layer, and an overcoat layerand wherein the overcoat layer is interposed between the fiber bundlelayer and the cathode layer.